FIG. 3 is a schematic diagram of a conventional axial-flow gas laser oscillator. The conventional axial-flow gas laser oscillator is described hereinafter with reference to FIG. 3. In FIG. 3, discharge tube 901 is made of dielectric material, e.g. glass. Electrodes 902 and 903 are placed around discharge tube 901. Power supply 904 is connected to electrodes 902 and 903. Discharge space 905 exists within discharge tube 901 across electrodes 902 and 903. Total reflection mirror 906 and partial reflection mirror 907 are rigidly placed at both ends of discharge space 905, thereby forming an optical resonator. Laser beam 908 is output from partial reflection mirror 907. Laser gas flowing path 910 indicates the flow route of laser gas flow 909, which circulates within the axial-flow gas laser oscillator. Heat exchangers 911 and 912 lower the temperature of laser gas that is warmed up by a discharge in discharge space 905 and blowing parts 913 which circulates the laser gas within the oscillator. Blowing parts 913 effects a flow speed of the laser gas of approx. 100 m/sec in discharge space 905. Laser gas flowing path 910 and discharge tube 901 are merged together at laser gas inlet port 914.
FIG. 4 schematically illustrates a conventional gas laser processing machine specializing in cutting a sheet metal. This conventional machine is described hereinafter with reference to FIG. 4. As shown in FIG. 4, laser beam 908 is reflected by reflection mirror 915 and is led around work-piece 916. Then laser beam 908 is condensed into an enriched energy beam by condensing lens 918 placed in torch 917, and then work-piece 916 is irradiated with the beam, whereby work-piece 916 can be cut. Work-piece 916 is rigidly mounted on processing table 919, and X-axis motor 920 or Y-axis motor 921 moves torch 917 relative to work-piece 916, so that work piece 916 is processed into a given shape.
The foregoing description refers to the structures of the conventional gas laser oscillator 900 and the conventional gas laser processing machine. Next, operation of the conventional gas laser oscillator 900 is described hereinafter.
The laser gas transmitted by blowing parts 913 travels through laser-gas flowing path 910 before it is introduced into discharge tube 901 via laser gas inlet port 914. The laser gas then generates electric discharge in discharge space 905 from electrodes 902 and 903. The laser gas flowing through discharge space 905 gets excited by gaining this discharge energy. The excited laser gas then is optically resonated by the optical resonator formed of total reflection mirror 906 and partial reflection mirror 907. Laser beam 908 is output from partial reflection mirror 907. Laser beam 908 thus produced is used for the applications, e.g. laser beam machining.
In general, the laser beam oscillator employs a centrifugal blowing parts, and FIG. 5 shows a structure of blowing parts 913 used in the conventional gas laser oscillator. Motor-rotor 922 is mounted on rotary shaft 923, and impeller 924 is mounted to the end of shaft 923. Motor-stator 926 is placed coaxially with motor-rotor 922 and is fixed to casing 925. Supply of AC power from the outside to motor-stator 926 generates a rotary magnetic field, which rotates rotor 922, thereby rotating impeller 924 via shaft 923. Scroll 927 is placed around impeller 924, and the rotation of impeller 924 thus generates laser gas flow 909.
Rotary shaft 923 is rotatably supported by bearings 928 placed at the upper section and the lower section of shaft 923, to which bearings 928 are coupled. Blowing parts 913 is formed of a rotary part and a non-rotary part, and the rotary part includes motor-rotor 922, rotary shaft 923, impeller 924, and bearings 928.
Patent Literature 1 discloses related art to the blowing parts, and this related art refers to a three-axis orthogonal type laser oscillator, in which a discharge section and a blowing section are separated from each other, and a blowing parts accommodated in the blowing section can be taken out to the outside. (Refer to, e.g. Patent Literature 1.)
The conventional gas laser oscillator 900 discussed previously has the following problems: Blowing parts 913 of the oscillator is one of the components to be replaced periodically at user's site. A cumulative working time of the gas laser oscillator 900, in general, exceeds 50,000 hours, and blowing parts 913, e.g. is replaced with a new one when the cumulative working time reaches approx. 16,000 hours. Blowing parts 913 includes some components that deteriorate over long hours, and most of those time-varying components are included in the rotating part. Bearing 928 wears fast among others, so that the end of service life of bearing 928 indicates that blowing parts 913 needs to be replaced.
It is natural to replace only bearing 928 for a revival of blowing parts 913; however, the dismount of bearing 928 requires disassembling the entire blowing parts 913, and an adjustment of the balance of the rotary section is needed. These steps need special equipment as well as one week for calibration. For job-shops who are the main users of the gas laser oscillators, the maximum allowable time for a routine inspection is only a half-day. The users are, therefore, obliged to replace entire blowing parts 913. As a result, the cost of the routine inspection rises. In other words, a cost reduction in the routine inspection with respect to blowing parts 913 has been a vital problem.